It sounds like you are not building any sexual tension. Yes, you are confident and are trying out verbal game, but at the end of the day if you are not escalating sexually then none of that matters. Obviously, helps if you take or meet girls in a dark environment with alcohol...ie a bar..Lol from there, as you talk just touch her and lead lets go dance, lets get a drink, and just smoothly escalate, always invade her personal space to generate attraction and go for the kiss, following that give her a none sexual reason to go home with you, more likely she will go with that "you know, I have a great place, come on lets go, we can chill there for a bit, we can have a glass of wine" once the girl is back, chill, put some relaxing music on, get her a drink, slow down your words, hold eye contact, kiss her, once she is in your room she will switch to lets have sex mode and its on.... in terms of girlfriend once sex is out of the way, next day offer to take her home but stop off for some lunch.... basically keep in touch with her show that you are not just after sex. hope that helps.
Finally, its none of the words that get you the girl in my opinion, it has everything to do with your mindset, body language, voice, actions, leaderships, dominance... the words of worth like 5-10%
At your age as well be fun, and GO DIRECT... young women will appreciate that far more, a lot of advice from PUA gurus seems to lend itself to older women over 25... for the younger ones, telling her in a confident way, you are cute, who are you? will get you much further, you dont need all these routines.... just honesty, and a plan.... your cute, wanted to say hello, I'm thirsty, how about a coffee? actually, yes lets get a coffee, come on....
Depending on when you meet the girl in the day or night, remember more so in the day, the pua thing can come across as weird and creepy to women, so make sure that you demonstrate an understanding of this for example after doing what I said earlier asking her for a coffee, say sorry I know its really random but you only live once, and I have to meet a friend in like an hour, so why not right...
Examples of good direct approaching and body language watch this!!!
http://www.youtube.com/watch?v=tlWrFgIR6CU